NOVEL DIPORPHYRINS CONTAINING N4 AND N3S CORES - SYNTHESIS, CHARACTERIZATION, AND ELECTROCHEMICAL PROPERTIES

Novel diporphyrins containing a meso-tetraphenylporphyrin (TPPH2) with an N4 core and a core-modified monothiaporphyrin (STPPH) with an N3S core covalently joined through a short alkyl chain at the para positions of meso phenyl rings have been synthesized and characterized. H-1 NMR and optical spectral data indicate a weak interaction between the two porphyrin subunits for H-2-H and Zn-H diporphyrins. However, in the Zn-Cu and Ni-Ni diporphyrins there is substantial interaction between the two subunits induced by the structural change caused by introduction of metal to the thiaporphyrin subunit. This is reflected in the optical absorption band and redox potential shifts. Furthermore, the geometries around the two metals in these diporphyrins are different because of the difference in the electronic structures of the two porphyrin rings. Electrochemical studies on Zn-Cu and Ni-Ni diporphyrins indicate the reduction of the metal center present in the thiaporphyrin subunit at very low potentials (-0.0885 V for Cu(II)/Cu(I) and -0.28 V for Ni(II)/Ni(I)) suggesting that the metal d(x2-y2) orbital is lower in energy relative to the e(g)(pi*) orbital of the thiaporphyrin ring. This observation suggests the possibility of stabilization of different oxidation states of the same metal in homobimetallic and different metals in heterobimetallic diporphyrins.